For decades, the U.S. Navy has used high-powered sonar during anti-submarine training and testing exercises in various ocean habitats, including the San Nicolas Basin off Southern California. Beaked whales are particularly sensitive to these kinds of military sonars, which sometimes result in mass stranding events. Following legal action from environmental activists related to these risks, the Navy modified some training activities, created "sonar-free" areas, and spent more than a decade and tens of millions of dollars trying to find ways to reduce the harm to beaked whales and other mammals.

The new research, led by Brandon Southall at the University of California, Santa Cruz, and Kelly Benoit-Bird at the Monterey Bay Aquarium Research Institute, aimed to better understand why whales keep returning to the test range despite the risks.

Researchers - Robot - Echosounders - Abundance - Density

The researchers equipped an underwater robot with echosounders to measure the abundance, density, and sizes of deep-sea squids in different parts of the Navy test range, as well as in nearby waters. They also developed an "energy budget" for beaked whales, showcasing the costs -- in time and calories -- of hunting for squid. This helped the researchers estimate how many dives the whales needed to make in order to get enough food to survive in different areas.

"Beaked whales work very hard to obtain their food. They are essentially living paycheck to paycheck," said Benoit-Bird. Unlike many baleen whales with significant energy reserves, beaked whales can't afford to expend too much energy on a dive that doesn't result in capturing many squid. In areas where the concentration of prey is low, the beaked whales must work harder and expend more calories -- making reproduction and raising young that much more challenging. Some of the areas under study were so poor in terms of prey that whales likely could not meet their basic energetic...